Field of the Invention
The invention relates in general to a supply modulator, a power supply circuit, and an associated control method, and more particularly to a supply modulator, a modulated power supply circuit, and an associated control method for providing a modulated voltage to a power amplifier.
Description of the Related Art
FIG. 1A (prior art) is a block diagram illustrating supplying a supply voltage to a power amplifier based on a fix drain bias approach. In FIG. 1A, the power amplifier (PA) 11 operates based on a supply voltage Vdd having a constant DC value. After receiving an input signal Sin, the power amplifier 11 amplifies the input signal Sin to generate an amplified output signal Sout.
FIG. 1B (prior art) is a schematic diagram illustrating power supplied to and consumed by the power amplifier based on the fixed drain bias approach. The horizontal line Ln1 represents that the supply voltage Vdd supplied to the power amplifier 11 is constant, In FIG. 1B, the area shown with oblique lines (Ppa) represents actual power consumption of the power amplifier 11, and the area shown with dotted screentone (Pa1) represents the power which is provided to but not utilized by the power amplifier 11, Therefore, the area shown with dotted screentone (Pa1) implies the unnecessary power loss in the power amplifier 11.
As shown in FIG. 1B, the fixed drain bias approach employs a fixed supply voltage Vdd to the power amplifier 11, but the power consumed by the power simplifier varies all the time. In consequence, the fixed drain bias approach results in considerable power loss and brings thermal issues.
The supply voltage Vdd is provided by a voltage source, typically a battery. As the fixed drain bias approach is not power efficient, battery life becomes shorter. Therefore, an efficient approach to reduce unnecessary power dissipation is desired.